A conventional projectile ball B as shown in FIG. 1 is wound thereon with two Velcro tapes V crossing with each other. The ball B will be thrown onto a target T having coarse surface formed on the target T to attach the ball on the target by fastening the Velcro tapes V on the ball B with the coarse surface on the target T.
However, the two Velcro tapes V wound on the ball B may be easily loosened and released from the ball B of spherical shape to lose its fastening effect, thereby being unable to be fastened to the coarse surface of the target T whenever throwing the ball to the target.